The invention is particularly applicable to video signal processing using compression and decompression and may be used with the MPEG video decompression system. In such a system a video signal generator forms video signals representing successive frames of an image and the signals are compressed by known techniques prior to transmission to a receiving station. At the receiving station the compressed signals are decompressed, for example by the formation of the Inverse Discrete Cosine Transform. The video data representing each image frame is provided by three separate channels. The first channel herein referred to as the Y signal is a luminance channel representing the luminance at full resolution of all picture elements in the frame. The other two channels are chrominence channels herein referred to as U and V channels respectively. These channels indicate colour difference signals for picture elements and the chrominence signals are provided at half resolution in each of the X and Y directions thereby resulting in quarter resolution for the whole frame. The decompressed data representing selected image frames is stored and used to predict video signal values for intermediate video frames. To calculate the predicted frames it is sometimes necessary to input data representing a selected area of the frame together with data representing the image half a picture element displaced from the selected area possibly in both the X and Y directions. The processor used to calculate the predicted frames may load data from a memory storing the frame video data into a temporary store and the transfer of data into the temporary store representing the selected area and the half picture element displacement from the selected area may involve a large number of data transfer operations into the temporary store.
It is an object of the present invention to provide improved video signal processing apparatus and method which can be used to simplify data transfers in processing video signal data.